Quantity of 2 ($15 each) unused float glass panes for sharpening, and flattening the backs of, smaller blades like chisels and plane blades.
Each is 4 1/2” wide by 14” long by 7/16” thick.
Float glass provides a very flat surface. You can put various (adhesive-backed) sandpaper grits on it, then use as part of a sharpening set up.